Method and device for assessing muscular capacities of athletes using short tests

ABSTRACT

Device ( 1 ) for measuring muscular capacity, comprising:
         removable fastening means ( 12 ) for fastening the device to the athlete or to the moved weight ( 3; 2 );   autonomous electrical power supply means ( 15 );   a display ( 11 );   a three-axis accelerometer ( 14 ) for delivering a sequence of accelerations (a(t)) along the axis of movement of the weight, said sequence comprising at least 100 measurements per second over a duration between 1 and 10 seconds; and   data processing means ( 16 ) for determining, at the end of the test, on the basis of said sequence of accelerations, at least one quantity representative of the muscular capacity of the athlete and for displaying this quantity on said display ( 11 ).

The present invention is a continuation of International ApplicationPCT-EP 2007-052413 filed on Mar. 14, 2007 and published under the numberWO 07/107,491, the content of which is incorporated here by reference.This application claims the priority of European Patent ApplicationEP07111352, filed on Mar. 17, 2006 and published under the numberEP1834583, the content of which is incorporated here by reference.

TECHNICAL FIELD

The present invention relates to the field of methods and devices forevaluating muscular capacity, especially for sport and forrehabilitation. The present invention relates in particular to devicesfor evaluating muscular physiological parameters, for example muscularpower and force, these being based on acceleration measurements.

PRIOR ART

Performance measurement apparatus is being increasingly used for thetraining of athletes and for rehabilitation after an accident. Forexample in cardiovascular training (jogging, cycling, etc.), the use ofheartbeat meters (“pulsometers”) and pedometers has grown substantiallyin recent years. Such portable apparatus takes measurements duringexertion, enabling the athlete to adapt the training using objectivedata. The measured quantities delivered typically indicate the heartbeatrate, the distance traveled, the duration of training, the average ormaximum speed, etc. However, they do not provide any direct measurementof the muscular power of the athlete or of a muscular chain of theathlete.

U.S. Pat. No. 5,788,655 (Omron) describes an apparatus intended to befixed to the body and provided with an accelerometer and an LCD display.The apparatus permanently measures the movements of the wearer in orderto determine his level of physical activity and othermetabolism-dependent quantities, for example the daily calorieconsumption of the user. This type of apparatus is useful for measuringthe level of sedentariness of patients more objectively. However, it isunsuitable for muscular training and for measuring brief exertions, andis unable to determine for example the maximum power of an athlete'smuscle group.

WO 2005/074795 (Nokia) describes a measurement terminal provided with anaccelerometer, the terminal being attached to the body of an athlete.The measurement data is evaluated so as to provide a quantityrepresentative of the intensity of exertion delivered. Again, theobjective is to determine the level of activity over a long period, forexample a day or a week.

WO 03/032826 (Philips) describes a similar system, provided with athree-axis accelerometer for determining the level of physical activityof a patient. The proposed device displays quantities such as the dailymetabolic rate, the daily energy expenditure or the energy expenditureinduced by exercise. This apparatus is therefore useful for measuringaccelerations over a period of several hours, or even several days.

The devices of the type described above are therefore suitableessentially for measuring activity during lengthy exercising, forexample over the course of a jogging session, a badminton match or anordinary day. There are also quite similar devices for detecting fallsby the aged, the time that they spend sitting down, standing up or lyingdown, etc.

However, there is also a need to measure parameters during brief or verybrief muscular exertions. For example, muscular training and measurementof muscular capacity of athletes often involve very short movements, forexample a single lift of a weight on a muscle-development machine, or asingle jump. The sampling frequency employed by the above devices doesnot generally allow them to be used for measuring kinematic parametersover so brief an exertion. Moreover, the data calculated from themeasured accelerations are of little interest for short exertions. Forexample, it is of little interest to know the amount of calories burntoff during a single movement. However, there is a need for apparatussuitable in particular for muscle development, enabling for example theincrease in force or power of a muscle or muscle group being exercisedto be measured.

Already known in the prior art are certain measurement devicesspecifically intended for training and for measurement of briefmovements. For example, U.S. Pat. No. 5,474,083 describes a systemintended for monitoring weight-lifting movements by a patient. Thesystem employs electrodes for measuring the activity of the patient'smuscles during the movement and also a weight movement detector. Analarm is triggered in the event of an inappropriate movement. Thissystem is useful for preventing accidents caused by lifting weightsincorrectly or for training people to lift weights without hurtingthemselves. However, it is inappropriate for measuring the muscularperformance of a sportsman. Moreover, the use of electrodes makes it notvery practical to use.

U.S. Pat. No. 6,397,151 describes a wristwatch device comprising anaccelerometer for measuring a sequence of accelerations of the forearmduring a blow in a martial arts sport. The force exerted is thencalculated. The accelerometer measures an acceleration along a singleaxis, which must be perfectly aligned with the direction of movement ofthe forearm. If the wristwatch device moves during the blow, theaccelerometer measures only the component of the force along thedirection of the accelerometer.

US 2004/134274 describes a device for measuring muscular force. Thedevice includes an inclinometer for measuring its angle of inclinationand for obtaining the force along a chosen direction. Inclinometers areexpensive and sensitive mechanical devices.

U.S. Pat. No. 6,148,280 (Virtual Technologies) describes a deviceprovided with accelerometers and gyroscopes placed over the entire bodyof an athlete. The data delivered by several sensors is transmitted to apersonal computer, which enables the trajectory and othercharacteristics of the movement to be analyzed. This system is complex,as it employs several sensors, including expensive goniometers, whichare relatively fragile. Connecting the sensors together and to theexternal computer makes the device expensive and awkward to install. Itis suitable for precise movement training, for example a golf swing, butdoes not allow direct determination of the muscular capacity developedby the sportsman during this movement.

DE 446302 describes an accelerometer used in combat sports to measurethe acceleration of the striking surface. The apparatus is not portableand is suitable only for combat sports, such as boxing, karate, etc. Anexternal computer has to be employed in order for the measurementresults to be evaluated and displayed.

Other devices based on accelerometers and gyroscopes exist, enabling forexample the trajectory of a golf swing to be monitored so as to improvethe movement. U.S. Pat. No. 5,056,783 describes for example a baseballbat provided with a three-axis accelerometer in order to specify themovement of the bat in space. This type of device delivers a largeamount of data, for example the position and speed of the sensor at eachinstant, often requiring a large screen or an external device to displaythis data. However, such devices are unable to calculate and immediatelydisplay thereon one or more quantities representative of the athlete'smuscular capacity.

BRIEF DESCRIPTION OF THE INVENTION

The aim of the present invention is to provide a measurement method anda measurement device enabling the muscular capacity of athletes to beevaluated. The aim of the present invention is to propose a rapid testwith an instrument which is simple to use, is autonomous andinexpensive, and capable of immediately delivering data representativeof muscle-related qualities of athletes, for example their explosivepower, power, muscle relaxation, etc.

One object of the present invention is to provide a sports performancemeasurement apparatus specifically intended for training and for musclerehabilitation, involving for example known muscular tests such asjumping or weightlifting tests. In particular, the device must enablerelaxation, explosive power and force enhancement (FE) of athletes to beevaluated by means of brief noninvasive tests.

According to the invention, these objectives are achieved in particularby means of a method of evaluating the muscular capacity of athletesusing brief tests, such as lifts and/or jumps, comprising the followingsteps:

-   -   a removable and electrically autonomous measurement device is        fastened to a weight that moves during the test, said        measurement device being based on a three-axis accelerometer;    -   a sequence of successive accelerations of said weight is        determined during said test; and    -   at the end of said test, at least one quantity representative of        said muscular capacity, which is determined from said sequence        of accelerations, is indicated on said display.

The muscular capacity may be calculated and displayed at the end of thetest, for example in the form of the maximum power, the forceenhancement, etc.

The three-axis accelerometer is used to determine the vertical gravitydirection, and therefore to obtain the direction of the accelerationalong this direction or along any chosen direction correspondingpreferably to the direction of displacement of a weight. In a preferredembodiment, the quantity representative of the muscular capacity isdetermined from a sequence of accelerations along a single axis, forexample along the vertical axis during a vertical jump, or along theaxis of displacement of the weight. The vertical direction and theorientation of the accelerometer in space are preferably determined inadvance, for example during a calibration phase, during which theaccelerometer must be kept stationary. Visual and/or audible signals maybe emitted during this calibration phase so as to ask the user to keepthe accelerometer stationary and oriented as at the start of theexercise.

The device is suitable for measuring acceleration as a function of timeand for evaluating the results, for example during the execution of thefollowing tests:

-   -   a weight lift;    -   a squat jump and/or countermovement jump;    -   a drop jump.

Other tests, including core (abdominals) training tests, bench presstests, plyometric tests, etc., may be employed.

The calculation of the displayed quantities takes into account the apriori knowledge of the form of the acceleration function during thesestandardized muscular tests. The device uses this prior knowledge todetermine quantities that a generic device would be unable to measure.For example, the device of the invention may, in one embodiment,decompose a movement into key phases and calculate the maximum powerduring one particular phase. For example, a jump may comprise a muscleextension phase followed by a flexion phase. The device is able tosegment the measured data so as to determine the start and end of thesetwo phases, and then to calculate for example the power during extensionand the maximum rate during flexion.

Typically, the device must be capable of acquiring acceleration dataalong three axes, at least every 100th of a second, during a briefexertion, i.e. an exertion lasting typically less than 10 seconds, butpossibly lasting up to several minutes.

The use of a three-axis accelerometer enables the acceleration along anydirection to be calculated, especially along the weight displacementdirection, for example the vertical direction in a jump. In a preferredembodiment, only a sequence of accelerations along this preferentialdirection is used to calculate the quantities displayed.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are indicated in the descriptionillustrated by the appended figures in which:

FIG. 1 illustrates schematically various movement phases of an athleteduring a weight lift of the “bench press” type;

FIG. 2 illustrates the height of the weight lifted as a function of time(h(t)) during the bench press exercise illustrated in FIG. 1;

FIG. 3 illustrates the speed of the weight lifted as a function of time(v(t)) during the bench press exercise illustrated in FIG. 1;

FIG. 4 illustrates the acceleration of the weight lifted as a functionof time (a(t)) during the bench press exercise illustrated in FIG. 1;

FIG. 5 illustrates the maximum force, the maximum speed and the maximumpower that an athlete can deploy as a function of the weight moved;

FIG. 6 illustrates the acceleration a(t) as a function of time during anexercise;

FIG. 7 illustrates a squat jump test;

FIG. 8 illustrates a countermovement jump test;

FIG. 9 illustrates a drop jump test;

FIG. 10 illustrates a device for evaluating muscular capacity accordingto the invention;

FIG. 11 is a block diagram showing the main electronic components of thedevice of FIG. 10;

FIG. 12 is a flowchart illustrating the parameterization of the device;and

FIG. 13 is a flowchart illustrating the muscular capacity test duringthe method.

EXEMPLARY EMBODIMENTS OF THE INVENTION

FIGS. 1 to 4 illustrate the change in various kinematic parametersduring a weightlifting movement of the bench press type. This movement,widely used in muscle development, consists in lifting a weight 2 withboth arms, starting from a position in which one's back is lying on abench. The weight is lifted as high as possible, combining adduction ofthe shoulder and extension of the elbow. FIG. 1 illustrates five keyinstants during the test. The test starts at T1, in the initial positionillustrated in the first image on the left of FIG. 1. The weight is atits lowest point, the athlete's elbows 3 being bent.

During phase A, between the instants T1 and T2, the athlete 3 lifts theweight, the velocity of which steadily increases, as indicated in FIGS.2 to 4. The thrust force deployed during this phase is a maximum and thearms are extended.

During phase B, between the instants T2 and T3, the thrust continues,but the lift velocity decreases—the acceleration therefore becomesnegative, as may be seen in FIG. 4. The weight is at the maximum heightat the point T2.

The athlete then relaxes his exertion during phase C between the keyinstants T3 and T4. The weight is lowered slightly, so that its velocitybecomes negative. This step is followed by a stabilization phase D,between the instants T4 and T5, during which the athlete keeps his armsextended, but tends to lower the shoulders. The acceleration undergoneby the weight 2 during this phase tends progressively toward 1G (earth'sgravitation).

The key instants T1 to T5 may be determined unambiguously from the dataa(t), v(t) and h(t). As will be seen, these quantities can be measuredduring the exertion by means of a device 1 attached to the weight,ideally placed at the center of mass, and will be used to determine anddisplay the muscular capacity of the athlete.

FIG. 5 illustrates schematically one possible change in the maximumforce F_(max), in the maximum velocity V_(max) and in the maximum powerP_(max) that an athlete can deploy when lifting a weight of variablemass. The gravitational force (m×g) exerted on the weight deployedincreases linearly with the mass of the weight.

In contrast, the force (m×a) exerted by the athlete to pull this massagainst gravity depends directly on the force with which the athletemoves the weight. This is because the athlete has the possibility ofmodifying the acceleration imposed on the weight.

The maximum lift velocity V_(max) tends to decrease with increasing massof the weight lifted—the athlete lifts light weights more rapidly. Themaximum power P deployed by the athlete during the exertion isdetermined by the formula:

$P = {\frac{E}{t} = {{F \times v} = {m \times a \times v}}}$

This formula is valid for the case in which the acceleration and thevelocity are parallel to each other, for example during a purelyvertical movement. In the case of nonparallel vectors, the calculationmust be carried out vectorially.

The maximum power P_(max) during the exertion generally passes throughan optimum for a given value of m. A very heavy bar for an athlete willengage an athlete essentially in opposing stresses, i.e. for opposingthe gravitational force mg, and little in acceleration stresses ma (thebar is raised more slowly). Thus, it may be seen that by knowing themaximum power, as can be obtained by measuring the acceleration andvelocity of the weight, it is possible to determine the optimum weightwith which the athlete must train in order to maximize the powerdeployed during the exercise.

FIG. 6 illustrates the change in acceleration a(t) over the course oftime during a typical brief exertion, for example a lift or a jump.During the first phase of duration ΔT between the instants T0 and T1,the acceleration increases by Δa. If the weight lifted is constant, theacceleration is proportional to the force. The force enhancement (FE) orexplosive power, employed as a sport measurement, is therefore simplyproportional to Δa/Δt. The force enhancement is also proportional to thepower deployed by the athlete, at least when the distance h traveled bythe weight is constant.

It is also possible to determine the instantaneous power P(t) from thevalue of da/dt at each point on the curve a(t) and to determine themaximum power P_(max)(t)=max(P(t)). This value is however more sensitiveto errors and to the measurement noise—smoothing the curve a(t) by meansof a noise filter is useful for reducing spurious effects.

FIG. 7 illustrates another test used to determine the muscular capacityof an athlete 3. This test, called a “squat jump”, is intended inparticular to evaluate the relaxation of athletes, in particular dryrelaxation, without stretching, and their capability of developing ahigh force in a very short time (explosive power). The athlete startswith knees bent at 90° and hands on his hips, and then attempts to jumpas high as possible. A high initial acceleration is essential to reach agreat height.

A similar test, called the “countermovement jump”, is illustrated inFIG. 8. In this test, the athlete starts in a standing position (legsstraight) and is permitted to perform a flexing movement before theextension and jump. The difference between the result obtained in asquat jump and the normally higher height obtained in a countermovementjump depends on the muscular elasticity of the athlete and/or on hiscapability of developing a greater force during the damping.

Similar tests may be performed in which the athlete is permitted toswing his arms during the jump, in particular so as to check thecoordination between arms and legs. The quality of the rebound may bemeasured by multiple jumps, generally carried out on the spot, using thearms to help. Sometimes squat jump and countermovement jump tests arealso carried out with a weight on the athlete's shoulders.

The drop jump illustrated in FIG. 9 consists of a jump upward after theperformer has dropped down from a known height. The impulse is thereforepreceded by substantial tensioning which causes the tendons to stretchand different stressing of the muscles. The best athletes thus increasetheir jumping performance. In general, the test is performed with a 20cm, 40 cm, 60 cm and 80 cm drop in order to determine the correctworking height for each subject.

The jumps mentioned above may be decomposed into distinct phases,separated by key instants. Typically, a squat jump comprises thefollowing phases: start, call, impulse, flight, contact, bounce damping,end.

The above tests may be repeated, for example by performing a series of10 jumps or 20 lifts, so as to measure for example the change inmuscular performance and fatigue resistance of the athlete. One methodof use and/or indications on the display of the device preferablyindicate the number of tests to be performed. The device can then,depending on the test, perform calculations based either on the averageof the successive tests in a series, or on the best test or tests in theseries, or on certain predetermined tests in the series, for example byeliminating the first and/or last one(s).

It is also possible to carry out muscle asymmetry measurements, on thearms or the legs, for example by firstly performing a lift with the leftarm or the left leg and then with the corresponding right limb. Finally,certain tests enable imbalances between muscles or groups of muscles tobe measured, for example a difference in abnormal force between bicepsand triceps. These various tests involve several consecutivemeasurements, which can be stored in memory and then compared with oneanother. The result of the comparison may be displayed, for example inthe form of a percentage, for example 20% of the power differencebetween left leg and right leg. In the prior art, the performance ofathletes in the jump tests described above is often determined using acontact mat which starts a timer when the athlete leaves the mat andstops it when he returns to the ground. The suspension time allows theheight reached by the athlete to be determined. These devices howeverare bulky, expensive and enable the desired data to be obtained onlyindirectly, based on duration measurements.

The small screen of the device does not allow very detailed resultscalculated to be displayed. In one embodiment, only summarized resultsare displayed on the device, for example the maximum power. Moredetailed results, including for example the sequence of accelerationvalues along the weight movement direction, or along any otherdirection, may be displayed and processed by connecting the device to anexternal computer, for example via a USB connection or the like.

According to the method of the invention, a more significant measurementis obtained by linking the athlete 3 to a device 1 provided with athree-axis accelerometer, enabling the vertical acceleration of theathlete during the weight lift or the jump to be measured. In general,the three-axis accelerometer enables the component of the accelerationalong the weight movement direction to be measured.

An example of a suitable device 1 is illustrated in FIG. 10. The device1 comprises a casing, for example a plastic casing weighing less than100 grams, preferably less than 50 grams (including the contents), whichthe athlete can attach, depending on the exercise performed, to his bodyor to the weight lifted using removable fastening means 12, for examplea Velcro strip, a belt, etc. In a variant, the device is simply slippedinto a pocket of the garment worn, said pocket being designed for thispurpose and being narrow enough to keep the device in position. Thefastening means are then simply formed by the shape and the dimensionsof the external casing. The casing is preferably sealed and allows usein the open air, being resistant to the athlete's sweat. The fasteningmeans 12 preferably comprise a belt for fastening the device close tothe athlete's center of mass, for example to his hips or to his waist,or preferably level with the sacrum, in a slightly inclined positionduring the exertion. Trials have in fact shown that a belt 12 arrangedfor supporting the device on the sacrum minimizes the influence of thetrunk's movements in the anteroposterior direction. The maximum width ofthe belt is preferably large, for example greater than 10 centimeters,so that it is held in place better and prevented from being shifted bymovements of the skin and flesh over the skeleton.

In a variant, the fastening means enable the device to be fastened to anexisting belt. However, it is essential to make sure that a belt is usedthat does not move during exercises. Fastening the device to one's wristis however ill-suited for most muscle development tests, especially thetests described above, because the accelerations of the arms or wristadd to the accelerations of the body and because the wrist does notremain vertical during most of the exertions.

The device further includes a display 11, for example an alphanumeric ormatrix liquid-crystal display screen, for displaying control menus, thestate of the memory, the state of the battery, and also numericalquantities determined during or after the test. Control members 13, forexample buttons and/or members for moving a cursor, make it possible tonavigate the menus displayed, to select options to input data and toselect the results displayed. In a preferred embodiment, the device hasfour buttons for navigating the menus, these being placed around acentral confirm button.

FIG. 11 is a block diagram illustrating the main electronic componentsof the device 1. Apart from the external members already described inrelation to FIG. 10, it includes a three-axis accelerometer 14, forexample an accelerometer made in the form of a MEMS component and linkedto an analog-digital converter 140, or directly integrating such aconverter, so as to deliver sequences of acceleration measurements alongthree axes. The accelerometer 14 may have one or more preferential axes,offering greater precision, resolution and/or measurement range than inthe other axes. This preferential axis will preferably be alignedvertically when the device is in its normal use position, so as toimprove the measurement in the vertical direction. The measurement rangeof the preferential axis or axes is preferably greater than ±8 G, oreven ±10 G. The resolution of this axis is preferably greater than 10 oreven 12 bits. Preferably, the device does not contain a gyroscope, so asto reduce its cost, its consumption and the volume of data generated.The use of a one-axis gyroscope, or even a three-axis gyroscope, couldhowever be envisioned for certain types of muscular capacity test, orfor calibrating the vertical position more certainly.

The device 1 is preferably electrically autonomous, supplied for exampleby means of a battery 15 or a storage battery that can be recharged, forexample via the USB connection 19, or by removing it from the casing.The battery 15 supplies in particular a micro-processor 16 or amicrocontroller provided with a RAM and/or EEPROM memory 160. Themicroprocessor executes a program preferably containing EEPROM, and ableto be replaced via one of the interfaces, in order to analyze themeasurement data delivered by the accelerometer 14 and to control thedisplay 11 so as to display the desired quantities. An external memory,for example a RAM memory and/or a flash memory, may also be employed. Itis also possible to employ interchangeable flash memories, for exampleof the following types: CompactFlash, SD, MemoryStick, etc., so as totransfer data or programs more rapidly between the device and anexternal computer.

The device 1 also includes a real-time clock (RTC) 20, in particular formeasuring time intervals Δt, and also a buzzer 17 or a loudspeaker forgenerating alarm signals or other sounds. An input/output module (UART)162 is used to exchange data between the microprocessor 16 and externaldevices, for example for reprogramming it or for transmittingmeasurement results to a personal computer, a mobile telephone oranother external data processing device. The module 162 also makes itpossible to introduce, at any time, the parameters for new types of testand to determine the way in which the measurement data for these newtests will be exploited, so as to extract the desired representativequantities therefrom.

The module 162 is linked to an interface 19, for example via a USB ormini-USB connection, a wireless interface of the Bluetooth type or thelike, etc. The interface 19 is used in particular to recharge thebattery, to connect the device to an external computer, to reflash thefirmware of the microcontroller and/or to load new tests and newphysical exercises into the device.

FIG. 12 is a flowchart of the setup program, which is automaticallyexecuted when the device is first used, or on request by the user. Thesetup program is preferably stored in the EEPROM memory 160 and executedby the microprocessor 16. It starts from step 100 before the routine 101is executed, during which the user has the possibility of inputtinginformation stored permanently in the device. During step 102, the usercan input his identification (user ID or username) and possibly anoptional password so as to make the device unusable for a possiblethief. During step 103, the user can input the preferred measurementunits (kg/cm or lb/inch), enabling him to define, in step 103, hisweight employed for calculating the force, the work and the power inparticular in the jump exercises.

The user can then input the current date and time, which will then bepermanently updated by the clock 20.

Other permanent data that can be input at this stage include for examplethe preferred language of the menus, the type of result displayed, thetype of exercise by default, etc.

The numerical data may be input for example by incrementing values bymeans of + and − keys, or using a numerical keyboard (not shown), or byany other means for inputting data.

The setup procedure terminates in step 106 and preferably passesimmediately into test mode, in order to test the athlete's muscularcapacity. The test procedure is illustrated by the flowchart in FIG. 13.

During step 201, the user is invited to choose from a menu the type oftest that he desires to perform. This step may be implicit if a defaultchoice is stored in the permanent parameters of the device; it is alsopossible to propose by default the last test performed. In a preferredvariant, the user is invited to choose from the following options, or toconfirm a proposed choice from these options:

-   -   1. Weight lift    -   2. Jump (squat or countermovement jump)    -   3. Drop jump.

The user is also invited to select or confirm parameters that aredependent on the type of test. In the case of a lift, he must thusindicate the mass of the weight in the default unit of the device. Inthe case of a jump, he may be required to confirm his own weight. In thecase of a drop jump, the device will invite him to input or confirm thedrop jump height and his own weight.

The actual test starts at step 203, during which the user (the athlete)presses a key, for example an “ENTER” or “START” key (not shown). Thedevice then determines during the calibration step 204 its orientationrelative to the vertical. To do this, the athlete is for example invitedusing a message on the display 11 to stand still for a certain timeinterval, for example at least 2 seconds. In this position, onlygravitation imposes an acceleration on the three-axis accelerometer 14.A reference frame conversion matrix is calculated during this step, soas to convert the measurements along the three axes in a reference framecorrectly oriented with respect to the vertical. If the accelerometerdetects that the user has moved during the calibration interval 204, thecalibration is rejected and a visual and/or audible error message issent to the display 11 and/or by the buzzer 17. The user is then invitedto restart the calibration. The same may occur if the orientation of theapparatus is excessively inclined in relation to the ideal verticalposition, for example if the vertical acceleration measurement dependstoo greatly on the results from the nonpreferential axes of theaccelerometer.

Other calibration methods and methods of determining the verticalposition may be envisioned, including methods based on an action by theuser, who may be invited to place the device on a strictly horizontalsurface, or against a vertical wall, or methods involving additionalsensors, for example a goniometer for determining the angle orinclination of the athlete's body, a multi-axis gyroscope, a groundsatellite receiver of the GPS type, etc.

In the case of successful calibration, an audible beep is emitted duringstep 206 so as to invite the user to perform the test. The audiblesignal produced may depend on the test chosen and may furthermore beaccompanied by a message on the display 11. The acquisition of asequence of acceleration data then starts immediately in step 207 andterminates in step 208, after a predetermined duration (for example 10seconds), when the memory of the device is full or when the user pressesa key on the device, for example a key marked “END” or “START/STOP”. Itis also possible to interrupt the data acquisition automatically,depending on the measured data, for example when the device determinesthat the athlete has returned to the ground after a jump and that hisvertical acceleration is again zero or equal to 1 G.

The acceleration is preferably measured along three axes, at least every100th of a second or preferably every 2 milliseconds. The threesequences of accelerations are stored in the memory of themicro-processor 16 and then converted into a single sequence ofaccelerations along the weight movement axis (generally the verticalaxis) employing the reference frame conversion matrix determined duringcalibration.

In a variant, the acceleration data along the three axes isprogressively converted by the processor or even directly by logic meanson the accelerometer into a sequence of vertical accelerations stored inthe memory. A data conversion before storage requires greater computingpower, but does enable the size of the storage memory to be reduced orthe maximum possible acquisition time for a given memory space to beincreased.

At the end of acquisition, or possibly already during acquisition, theprocessor 16 executes a routine 209 for calculating at least onequantity representative of the athlete's muscular capacity. Thecalculated quantity and the method of calculation may depend on the typeof test selected during step 201. To give an example, the followingquantities may be determined:

-   -   the maximum instantaneous power (max(P_(inst))) during the        exercise or one particular phase of the exercise (for example        during the initial vertical acceleration phase in a jump);    -   the maximum power during a time interval (ΔT) of predetermined        duration, for example the maximum power during n sampling        instants;    -   the maximum power during a predetermined phase of the test        between two key instants T_(i), for example the power developed        during the thrust, during flexion, or to keep the weight lifted;    -   the maximum force enhancement FE (explosive power) during the        entire test or during a specified phase of the test;    -   the maximum force deployed in the vertical direction during the        entire test or during a specified phase of the test;    -   the energy expended in the vertical direction during the entire        test, or during one phase of the test, for example in joules or        in calories;    -   the maximum velocity reached during the entire test, or during        any phase of the test;    -   the maximum height reached in a jump (tests II and III);    -   the duration of certain phases of the test, for example the        duration of contact with the ground in a drop jump or the        duration of flight in a jump;    -   the energy efficiency, for example in the form of the ratio of        work delivered by the athlete to the kinetic energy of the        weight moved;    -   the difference between the measured or calculated values after        several tests, for example so as to determine fatigue during a        repeated exercise, an imbalance between muscles, a left-right        asymmetry, an improvement in performance of the athlete, etc.        The quantity calculated after a series of exercises may for        example be expressed and displayed as a percentage;    -   etc.

It is also possible to display several quantities at the end of thetest. To reduce the volume and the weight of the device, a digital oralphanumeric display of small size and low consumption, for example afour-line alphanumeric display, will however be employed. Multiplequantities can then be displayed by navigating between several resultsscreens.

The calculation of some of these quantities may involve determining thetemporal position of certain key instants and the duration of the periodbetween two key instants. Examples of key instants T1 to T5 areindicated in FIGS. 1 to 4 in the case of a weight lift. In the case of adrop jump, the key instants will for example be the start, the firstcontact with the ground, the instant when the rebounding athlete leavesthe ground, the instant when the maximum height is reached and theinstant when the athlete rejoins the ground for the second time, afterthe rebound. The automatic determination of the key instants based onthe acceleration data therefore depends on the type of exercise selectedand on the a priori knowledge of the form of the sequence ofaccelerations, or at least a portion of this sequence. Frequently, thekey instants of a movement are the instants during which theacceleration, the velocity or the position pass through a particularpoint, for example a minimum, a maximum, a passage through zero, apassage through a particular value (for example a 1 G acceleration) or apoint of inflection.

It is also possible to determine the phases from which the displayedquantities are determined on the basis of the sign of certain valuesderived from the acceleration. For example, it is possible to choose todetermine the maximum acceleration of all instants during which thevelocity is positive, i.e. directed upwardly. The determination of thekey instants and of the phases of the movement may also depend on theacceleration data along the nonvertical directions.

The key instants and/or the duration between two key instants (“keyduration”) may also be displayed at the end of the test as an additionalquantity representative of the athlete's muscular capacity.

The measurement may for example be refused if the form of theacceleration sequence obtained does not correspond to the expected modelaccording to the type of test selected and if the measurement does notenable the desired quantities to be obtained. In this case, a visualand/or audible error signal is preferably issued, to invite the athleteto restart the test.

At the end of a conclusive test, one or more of the above quantities areimmediately displayed during step 210 on the display 11. Several itemsof data may be displayed on several lines or on several screens, betweenwhich the user can navigate. Calculated quantities may also be stored inthe device, for comparison with quantities calculated during othertests.

The user is then invited to validate the test during step 211, forexample by pressing an “ENTER” or “OK” key. If he refuses to validatethe test, he is invited during step 212 to restart, by returning to step203, or to interrupt the test, passing directly to step 213. The programpasses directly to step 213 when the user validates the results.

During step 213, the results of the validated tests are stored in asemi-permanent memory 160, preferably associating them with the user'sidentification, the date and time of the test and an identification ofthe test type. In a first variant, suitable for devices having a largememory, the entire sequence of acceleration data along an axis, or evenalong all three axes, is stored in memory.

This variant makes it possible for other quantities to be subsequentlycalculated from this sequence, or to transfer it via the interface 162and 19 to an external processing unit (PC, PDA, mobile telephone, etc.)for subsequent exploitation, or to calculate and display otherquantities and other graphs. The transfer can be carried outautomatically as soon as a connection is established with an externaldevice, or by selecting a command in a menu or by another deliberateaction by the user of the device 1.

A software application may be loaded into and executed in the externaldevice so as to calculate other quantities, to represent themdifferently or to extract therefrom information which is more completethan the basic information immediately displayed on the device. Thesoftware enables for example quantities to be displayed in graph form orto see them in relation to previous measurements on the same athlete, oron other athletes, or with the objectives of a training program, whichmay be downloaded from the Internet. This application may also makecustomized training suggestions, depending on the measurement resultsfor each athlete and taking into account the athlete's progress atseveral dated tests. The training program proposed may take into accountthe results obtained during various tests and at different dates.

The software also preferably makes it possible to classify or ordervarious test results using the metadata transmitted by the device,including the date and time of the test, the athlete's identification,identification of the type of test and possible identification of thedevice employed, and/or using additional data input by the operator inorder to classify and group the results.

The previous tests, which are no longer relevant or have beentransferred to the external processing unit, may preferably be erasedfrom the memory of the device 1, either automatically during transfer orstorage of new results, or by an explicit command input by the user.

In the above method, the acquisition of a new series of accelerations isrepeated in each test, for example at each jump or each lift. However, atest is often performed several times in succession with only the bestresult taken into account. For example, many sports trainers recommendmeasuring the best squat jump, i.e. the best jump from a series oftypically 3 jumps during a brief period. If the memory of the device soallows, it is possible to program the device so as to input, during asingle acquisition, the data from several consecutive tests. The devicecan then be programmed to distinguish the three jumps during themeasurement sequence and for example to determine automatically the bestone. This type of test also makes it possible to determine, using asingle sequence of accelerations, the fatigue or, on the contrary, theincrease in relaxation between closely spaced consecutive tests, andthus to display other useful information relating to the athlete'smuscle development.

The present invention also relates to a system comprising a measurementdevice 1, as described above, linked to a data processing medium,comprising a computer program for the external unit, such as a computer,PDA or telephone. The data processing medium may consist of a CD-ROM, asemi-permanent memory (flash, EEPROM, etc.), a hard disk, etc. Thecomputer program executed makes it possible, as indicated above, tocommunicate with the measurement device 1 and to perform additionalcalculations and to display additional information based on the datareceived.

1. A method of evaluating muscular physiological parameters of athletesusing a short test, such as lifts and/or jumps, comprising the followingsteps: a removable and electrically autonomous measurement device isfastened to a weight that moves during said test, said measurementdevice being based on a three-axis accelerometer; a sequence ofsuccessive accelerations of said weight is determined during said test;and immediately at the end of said test, at least one quantityrepresentative of said muscular capacity, which is determined from saidsequence of accelerations, is indicated on a display of the device. 2.The method of claim 1, which includes a step of converting the sequenceof accelerations along three axes, delivered by said three-axisaccelerometer, into a sequence of accelerations along the presumeddirection of movement of said weight.
 3. The method of claim 1, whichincludes a step of initially selecting the type of test from a listcomprising at least: a weight lift; a jump by the athlete, thedetermination of said displayed quantity depending on the type of testchosen.
 4. The method of claim 3, in which said list comprises at leastthe following tests: a weight lift; a squat jump and/or countermovementjump; and a drop jump.
 5. The method of claim 3, which includes a stepof inputting at least one parameter of the test from the followingparameters: the mass of said weight; the jump height; the weight of thesportsman.
 6. The method of claim 5, in which the parameter to be inputdepends on the type of test selected.
 7. The method of claim 3, in whichthe choice of quantity displayed depends on the type of test selected.8. The method of claim 7, in which the method of calculation of thedisplayed quantity depends on the type of test selected.
 9. The methodof claim 1, in which said displayed quantity is determined by takinginto account a priori knowledge of the form of at least one portion ofsaid sequence of accelerations.
 10. The method of claim 1, in which saidat least one displayed quantity comprises at least one quantityproportional to the maximum power deployed by said athlete during thetest.
 11. The method of claim 10, said maximum power being aninstantaneous maximum power.
 12. The method of claim 10, said maximumpower being a maximum power during a time interval of predeterminedduration corresponding to several sampling instants.
 13. The method ofclaim 10, said maximum power being a maximum power during a timeinterval between two key instants of the test.
 14. The method of claim1, which includes a step of automatically determining at least one keyinstant or a key duration of the test from said sequence ofaccelerations, said displayed quantity being determined by taking intoaccount at least one said key instant or key duration.
 15. The method ofclaim 14, in which the determination of said key instant or said keyduration depends on the type of test selected.
 16. The method of claim14, in which said key instant (T_(i)) or said key duration is displayedon said display.
 17. The method of claim 1, which includes a calculationstep and a display step for calculating and displaying, after said test,the maximum force enhancement.
 18. The method of claim 1, in which saidat least one displayed quantity comprises at least one quantityproportional to the maximum velocity of said weight during the test. 19.The method of claim 1, in which a sequence of accelerations and/or ofdata calculated from these accelerations is transmitted to an externalprocessing device for calculating and displaying other quantities orgraphs representative of said muscular capacity.
 20. The method of claim1, which includes a step of determining the vertical direction usingindications provided by said three-axis accelerometer.
 21. The method ofclaim 1, in which said test is a jump, in which a parameter proportionalto the mass of the athlete is input into said device, in which saiddevice is fastened to the waist or trunk of the athlete, in which thevertical direction is determined before the jump on the basis ofindications from said accelerometer at rest before the jump, and inwhich said displayed quantity is aimed at estimating the explosive powerof the athlete.
 22. The method of claim 1, in which said test is aweight lift, in which a parameter proportional to the weight lifted isinput into said device, in which said device is removably fitted so asto move with said weight, in which the vertical direction is determinedbefore the lift on the basis of indications from said accelerometer atrest, and in which said displayed quantity is aimed at estimating thepower of the athlete.
 23. The method of claim 1, in which the durationof said test is less than 10 seconds and in which a said acceleration ismeasured at least every 100th of a second.
 24. A method of evaluatingmuscular physiological parameters of athletes using short tests, whichcomprises the following steps: a removable and electrically autonomousmeasurement device is fastened to a weight that moves during the test,said measurement device being based on a three-axis accelerometer; thetype of test is selected from a list comprising at least one weight lifttest and at least one jump test performed by the athlete; a successivesequence of accelerations of said weight is determined during said test;a quantity representative of said muscular capacity is calculated on thebasis of the acceleration data along the presumed direction of movementof said weight; and said quantity is displayed.
 25. A test device,comprising: removable fastening means for fastening said device to amoved weight; autonomous electrical power supply means; a display; athree-axis accelerometer for delivering a sequence of accelerationsalong the axis of movement of said weight, said sequence comprising atleast 100 measurements per second over a duration between 1 and 10seconds; and data processing means for determining, at the end of thetest, on the basis of said sequence of accelerations, at least onequantity representative of the muscular capacity of the athlete and fordisplaying this quantity on said display.
 26. The device of claim 25,which further includes removable means for linking to a computer, a PDAand/or an external computer.
 27. The device of claim 25, which furtherincludes means for selecting the type of exercise performed from a listof several possible exercises.
 28. The device of claim 25, in which saidremovable fastening means are intended for fastening said device to theathlete's waist and/or trunk.
 29. The device of claim 25, in which saidremovable fastening means include a Velcro strip.
 30. The device ofclaim 25, said three-axis accelerometer having at least one preferentialmeasurement axis, the measurement results from which are affected lessby a smaller error than those of the good of the other two axes, saidremovable fastening means being designed to fasten said device byaligning said preferential measurement axis substantially with thevertical direction.
 31. A test device intended to be fastened to a movedweight, comprising: an autonomous electrical power supply; a display; athree-axis accelerometer for delivering a sequence of accelerationsalong the axis of movement of the weight; and a microprocessorprogrammed to allow selection of the type of exercise performed from alist of several possible exercises, to determine, at the end of theexercise, on the basis of said sequence of accelerations, at least onequantity representative of the athlete's muscular capacity and then todisplay this quantity on said display.
 32. A test device, comprising: aVelcro strip, for fastening the device to a moved weight; an autonomouselectrical power supply; an accelerometer for delivering a sequence ofaccelerations along the axis of movement of the weight; and amicroprocessor programmed to determine, at the end of the test, on thebasis of said sequence of accelerations, at least one quantityrepresentative of the athlete's muscular capacity and then to displaythis quantity.
 33. The device of claim 32, which includes a belt forfastening the device close to the center of mass of the athlete.
 34. Asystem comprising a device as claimed in any of the claims 25 or 31 anda data processing medium, comprising a computer program intended to beexecuted by an external processing unit for displaying additionalquantities on the basis of the data measured by said device.